The St. Louis front-liners had accounted for 40 of the teams' 44 goals heading into Friday. For a change, Brewer and Colaiacovo contributed offensively.
"All of the defensemen here have had a lot of opportunities, and nothing has gone in," Brewer said. "It's all going to change and it started tonight."
Brewer recorded his first point of the season in 18 games. Colaiacovo scored his third goal of the season, tops on the team among defensemen.
"Back-end production is essential to our success," St. Louis coach Davis Payne said. "Very, very important for our team."
Colaiacovo added an assist in the third period.
Brewer was so surprised by his goal, his first since April 9, that he temporarily forgot to skate by the bench and bump fists with his teammates in the traditional celebratory manner.
"It's been a long time. I guess I better get more familiar with everything," he said. "The main thing is we got the win and we really needed it. It kind of stopped the madness. Now, it's upward and onward."
St. Louis took control with its second-period outburst.
Brad Boyes popped in a rebound of a shot from the point by Pietrangelo for a power-play goal that made it 1-1 midway through the period. It was Boyes' fourth goal in four games and fifth of the season.
Just 51 seconds later, Colaiacovo gave the Blues the lead for good with a blast from the top of the circle. Brewer completed the three-goal spurt with a slap shot from the point to put St. Louis ahead 3-1.
"We just started playing our style of hockey," Boyes said. "It was important to come out and make something happen."
The spurt seemed to slow the Senators, who had controlled play in the first period.
"We just got away from some of the things that we did in the first period to be successful," forward Mike Fisher said. "Once they got some momentum, the game turned right around."
St. Louis' record for fastest three goals was set on April 3, 1995, when the Blues scored them in 49 seconds against Toronto.
This one was every bit as effective in turning around the game.
"It kind of took the wind out of our sails," Ottawa coach Cory Clouston said.
The Senators have converted 12 of 49 power-play chances after an 0 for 17 start this season. ... St. Louis G Jaroslav Halak sat out after allowing 19 goals in his last four starts. ... Blues winger Alex Steen played in his 400 NHL game. Ottawa forward Ryan Shannon skated in his 200th. ... St. Louis has won all six meetings against Eastern Conference opponents this season and has won its last 11 against the East.
Copyright by STATS LLC and The Associated Press
Arena: Scottrade Center Location: Saint Louis, Missouri
Referees: Justin St. Pierre, Dennis LaRue Linesmen: Michel Cormier, Vaughan Rody
Attendance: 19,150 (100.0% full)
Team Stat Comparison
Power Play Goals
Power Play Opportunities
Shots on Goal
Mike Fisher (5)
Assists: Daniel Alfredsson, Milan Michalek
Brad Boyes (5)
(Power Play) Assists: David Backes, Alex Pietrangelo
Carlo Colaiacovo (3)
Assists: David Backes, Brad Boyes
Eric Brewer (1)
Assists: T.J. Hensick, Vladimir Sobotka
Andy McDonald (5)
Assist: Patrik Berglund
Patrik Berglund (5)
(Power Play) Assists: Carlo Colaiacovo, Alex Pietrangelo